This invention relates generally to controllers for internal combustion engines, and in particular to a controller for a compression ignition engine.
Larger motor vehicles such as heavy trucks and buses may be powered by diesel engines. Before the advent of electronic engine controls, such engines contained what may be generally considered as mechanical governors. Various types of engine governing can be performed by mechanical governors. One of those types is isochronous, or all-speed, governing.
Electronic governing of diesel engines has been made possible because of advances in electronic technology and fuel injection technology. Isochronous governing has been carried over in certain electronic governing strategies. It is believed that one reason for do so was because many professional drivers of larger diesel-powered motor vehicles had become accustomed to vehicles whose engines had mechanical governors operating with that strategy, and a change in strategy in a new vehicle might be foreign, and possibly unacceptable, to some of those drivers.
It is believed that diesel engines are also enjoying increased use in smaller vehicles such as medium trucks. It is further believed that automatic transmissions are being increasingly used in such vehicles. Drivers of such vehicles may be individuals who have little or no experience driving the larger vehicles, such as heavy trucks and buses, but they may be familiar with driving smaller vehicles which have gasoline engines and automatic transmissions. It is believed that such drivers will feel greater comfort in driving a diesel engine vehicle having an automatic transmission when such a vehicle operates in a manner similar to the smaller vehicles with which they may be familiar.
In such smaller vehicles moderate depression of the accelerator pedal results in part throttle operation that is effective to accelerate the vehicle through successive upshifts on a fairly level road until a desired speed is reached. On an uphill grade, greater depression of the accelerator pedal is needed to accelerate the vehicle through successive upshifts.
It has been observed that an automatic transmission vehicle powered by a diesel engine which is governed by isochronous, or all-speed, governing does not accelerate in the same manner as a smaller vehicle powered by a gasoline engine. The extent to which the driver depresses the accelerator pedal determines the speed to which the engine will accelerate. Isochronous governing causes the engine to be fueled in an amount sufficient to provide whatever torque is needed by the engine load, within the torque envelope for the engine, for the particular engine speed corresponding to the amount of accelerator pedal depression.
Because the torque converter of the automatic transmission is coupled to the engine output shaft, the state of the torque converter has an effect on the load which the vehicle drivetrain imposes on the engine. When the speed absorption ratio of the torque converter is zero, no propulsion torque is being transmitted through the torque converter to the drivetrain and hence the engine cannot propel the vehicle. Depressing the accelerator pedal will increase engine speed, and above some increased engine speed, the torque converter will begin to convert engine torque to drivetrain torque that will begin to accelerate the vehicle. As the vehicle accelerates, the speed of the torque converter output shaft begins to increase toward the torque converter input shaft speed, and the speed absorption ratio begins to increase.
For a given accelerator pedal position in a vehicle having an engine that is isochronously governed, engine speed is inherently constrained essentially to a single speed when the engine is operating in a steady state. Hence, the engine will accelerate when the accelerator pedal is depressed and will settle at a speed corresponding to accelerator pedal position. However, the engine speed that results when the accelerator pedal is depressed to a certain extent may be insufficient to cause the transmission to upshift, in which case, the engine may tend to lug instead of upshifting to a higher gear that would allow continued acceleration of the vehicle to an even higher vehicle speed. Increased engine speed sufficient to cause the transmission to upshift can be obtained only by further depression of the accelerator pedal in an amount sufficient to cause the engine to operate at that increased speed. A driver who is familiar with gasoline-powered vehicles may find the need to further depress the accelerator pedal of such a diesel-powered vehicle objectionable because of the added pedal effort required on his or her part.
A known engine controller that is present in certain vehicles manufactured by the assignee of this invention is premised on isochronous speed regulation and utilizes engine speed as a setpoint that is subsequently processed with additional data for developing a proper fueling command to operate the engine at the corresponding speed. The processor contains programmed data correlating engine speed setpoint data with combinations of accelerator pedal position data and engine load data and processes accelerator pedal position data corresponding to the position of the accelerator pedal and engine load data corresponding to the load on the engine in accordance with that programmed data to develop the engine speed setpoint data. Actual engine speed is an input to a governor PID (proportional, integral, derivative) and engine speed error, meaning the difference between actual engine speed and the engine speed setpoint, is another input to the governor PID. The governor PID processes the inputs to develop output data representing a governed mass fuel input to the engine. The controller subsequently develops a corresponding pulse signal for operating the engine fuel injectors. The governor strategy embodied in that controller is premised on isochronous speed regulation.
The present invention relates to an improvement to a controller of the type just mentioned for enabling the controller to act like a load governor rather than a speed governor without altering the architecture or the basic strategy embodied in the controller. Rather than rearranging the existing fundamental design architecture, the invention accomplishes load governing by programming the engine speed setpoint data in correlation with combinations of accelerator pedal position data and engine load data in ways that cause engine speed setpoint data to change in ways that when processed by the existing PID governor, result in governed mass fuel input to the engine responding to accelerator pedal position in the manner of a mechanical load governor, rather than a speed governor.
Accordingly, generic aspects of the present invention relate to an engine controller and method for controlling a compression ignition engine that powers a motor vehicle containing an accelerator pedal for accelerating the vehicle, wherein a processor processes various data to develop fueling data for accomplishing governed fueling of the engine. The processor contains programmed engine speed setpoint data representing engine speed setpoints correlated with combinations of accelerator pedal position data and engine load data. The processor processes accelerator pedal position data corresponding to the position of the accelerator pedal and engine load data corresponding to the load on the engine to develop engine speed setpoint data which is further processed with actual engine speed data to develop the fueling data to cause the engine to operate within an envelope of prescribed speed subject to limiting to a maximum speed. The programmed engine speed setpoint data is correlated to the accelerator pedal position data and the engine load data such that the engine speed setpoint data, when processed with actual engine speed data to develop the fueling data, causes the engine to be load governed.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.